The present invention relates to disk drives and, in particular, to the writing of servo tracks on a disk within the disk drive.
A disk drive is a device that is commonly employed in computer systems to store data. Typically, a disk drive includes: (1) one or more disks that each have a plurality of concentric tracks on which data is stored; (2) a spin motor for rotating the disk or disks; (3) one or more heads that are each capable of writing and/or reading data to/from a track on a disk; (4) an actuator for moving the head or heads to a desired location adjacent to a disk so that data can be written to the disk or read from the disk; and (5) circuitry for transferring data between a disk and a portion of a host computer system that is exterior to the disk drive, such as a random access memory (RAM).
A disk drive also typically includes a servo system that operates to move a head over a defined track on a disk surface and maintain the head over the defined track until directed to move the head over a different track. The servo system maintains the position of the head over a defined track based upon information that is read from a servo track. In one type of drive, the servo tracks are embedded in or coincident with the user data tracks, i.e., the servo track and the user data track form a single physical track with the servo data interspersed among the user data. Typically, the servo track: (1) identifies the particular track over which a head is positioned; and (2) provides data from which the position of the head relative to the center line of the track can be determined. The identification of the particular track is primarily used when the head is being moved from one track to another track (which is commonly known as a seek operation) to determine when the head is positioned over the desired track. Once the head is over the desired track, the data indicating the position of the head relative to the center line of the track is determined and used to maintain the head over the desired track (which is commonly known as a tracking operation). For example, if the data indicates that the head is positioned to one side of the center line, the servo system causes the actuator to move the head towards the center line.
Presently, the servo tracks are written on the disk surfaces of a disk drive during the manufacturing process by a servo track writer. The servo track writer uses a xe2x80x9cpush pinxe2x80x9d to move the actuator arm and thereby position the heads for writing the servo tracks. To elaborate, the servo track writer uses the xe2x80x9cpush pinxe2x80x9d to move the actuator and, as a consequence, position the heads for the writing of first servo tracks (one per disk surface). Once the first servo tracks have been written, the servo track writer uses the xe2x80x9cpush pinxe2x80x9d to move the actuator and thereby reposition the heads for the writing of the second servo tracks. This process is repeated until all of the servo tracks have been written. As an alternative to using a servo track writer, the drive itself can be used to write the servo tracks in what is known as self servo writing. In this case, a motor associated with the actuator is used to move the actuator arm in discrete steps to write each servo track. In either case, for at least a band or section of contiguous tracks, the heads are either: (1) moved such that the arc that the heads move through from one track to the next track is substantially equal, which results in the track density changing over the band of tracks and is known as the xe2x80x9cequal-arc drive formatxe2x80x9d; or (2) moved such that the distance between adjacent tracks remains substantially constant over the band of tracks, which is known as the xe2x80x9cequal-length drive format.xe2x80x9d
Regardless of whether a servo track writer or self servo writing is used to establish the servo tracks in a drive or the track format (equal-arc or equal-length) used, the track density measured in tracks per inch (TPI) at a give radius is the same for all of the disk surfaces in the drive.
The present invention recognizes that the optimal servo track density at a given radius can vary from disk surface to disk surface within the drive and that the present methods of writing servo tracks do not provide for writing the servo tracks on different disk surfaces with different densities at a given radius. The present invention is directed to using a multi-stage actuator within the drive to write servo tracks on two or more disk surfaces within a drive with the track density on each surface at a given radius approaching the optimal track density for that surface. The multi-stage actuator includes a primary actuator for coarsely positioning a head and a secondary actuator for finely positioning the head.
In one embodiment, a disk drive includes at least two separate and substantially parallel disk surfaces that are capable of storing data. Associated with each disk surface is a head for transferring data between the disk surface and the exterior environment. A multi-stage actuator is used to move the heads to desired positions over the disk surfaces for the transfer of data. The multi-stage actuator includes a primary actuator for coarsely positioning the heads relative to the disk surfaces. Associated with each head is a secondary actuator that permits the position of the head to be more finely controlled. The data transfer circuitry of the disk drive, which is normally used to write/read user data to/from the disk, is also adapted to write the servo tracks on the track surfaces. Initially, the tracks per inch (TPI) format that is appropriate for each disk surface on which servo tracks are to be established is determined. While the TPI format may be the same for each disk surface, it is more likely that the TPI format will be at least slightly different for each disk surface. Typical measurements from which the TPI format for a particular surface is determined include the read head width, the write head width and off-track performance based upon a bit error rate and read channel quality factor. Once the TPI format for each disk surface has been determined, the primary actuator is used to position each of the heads for the writing of the first servo track on each of the disk surfaces. The secondary actuators are also used to position each of the heads for the writing of the first servo tracks. Once the heads have been positioned, the first servo tracks are written on each of the disk surfaces. After the first servo tracks are written, the heads are repositioned to write the second set of servo tracks on the disk using the secondary actuators. Because the secondary actuators are capable of operating independently of one another, a different TPI format can be implemented for each disk surface. Once most or all of the servo tracks that can be written for a given position of the primary actuator by using the secondary actuators to move the heads have been written, the primary actuator is repositioned and the process is repeated.
In one embodiment, the position of the actuator arm that carries the heads is adjusted using the actuator motor in a self servo writing operation. In this case, the actuator motor is used to position the actuator arm associated with the primary actuator.
In another embodiment, the position of the primary actuator and, more specifically, the actuator arm that carries the heads (as is part of the primary actuator) is adjusted by a servo writer. In this case, a xe2x80x9cpush pinxe2x80x9d associated with the servo track writer contacts the actuator arm and pushes the arm such that the heads are positioned over the desired locations on the disk surfaces.